1. Field of the Invention
The present invention relates to a magnetic recording medium utilized as an information recording medium, and a method of manufacturing the same.
2. Description of the Related Art
With recent rapid increase in information processing quantity, realization of large increase in capacity is required in magnetic recording media widely used as an information recording medium. Particularly, in hard discs, large increase in capacity and large increase in recording density have been realized until now with development of fine processing technology and signal processing technology, etc. being supported. However, nowadays, recording density is becoming close to about 200 Gbits/in2 which has been considered to be physical limit resulting from the problem of thermal fluctuation in the conventional in-plane recording system in which magnetization is recorded in a substrate in-plane direction, and increasing speed of the recording density becomes gentle. In recent years, hard discs of the system of recording magnetization in a substrate perpendicular direction, which is the so-called perpendicular recording system, which have been considered to be tolerable to the problem of the thermal fluctuation have been realized as products. From this fact, it is expected that further improvement in the recording density will be realized also in future.
However, with respect to realization of higher density in future, increase in noise becomes a great problem. Namely, there is the problem that unevennesses of shape and size of magnetic particle constitute cause of noise with miniaturization of recording bits based on realization of high recording density to deteriorate the recording/reproducing characteristic. To solve this problem, it is considered that reduction in exchange interaction between adjacent magnetic particles, and miniaturization of size of magnetic particle or realization of uniform shape are effective. Specifically, there are mentioned a method of adding SiO2 into CoCrPt based material to surround magnetic particle by non-magnetic material to separate the magnetic particle, and a method of reducing mean diameter of particles with respect to the recording direction.
Moreover, there is also known a method of controlling shape and size of magnetic particle by making use of the fine processing technology to thereby allow them to be uniform. Particularly, a medium in which control is performed to the extent of arrangement of magnetic particles is performed so that magnetic particles which are uniform in shape and size are regularly arranged is called a patterned medium. Thus, an ultra-high density recording medium having the recording density of the order of 1T bits/in2 can be realized.
To prepare such a patterned medium, there is mentioned a method of implementing processing such as etching, etc. to magnetic layer to prepare regularly arranged magnetic particles which are uniform in shape and size.
Moreover, in order to lessen damage to the magnetic layer due to physical processing such as etching, etc., there is also a method of chemically alter a part of the magnetic layer. Namely, there is proposed a method in which mask is provided on the magnetic layer surface to halogenate the exposed magnetic layer to thereby allow the exposed magnetic layer parts to be locally non-magnetized.
Further, there is also known a method of preparing an uneven structure in which projections are regularly arranged in advance thereafter to form films of magnetic material to allow the magnetic material parts formed as film on the upper surface of the projections to be as recording part.
However, in the conventional method of allowing the magnetic layer parts to be locally non-magnetized by a chemical process, it is difficult to obtain sufficient processing accuracy because the size of magnetic particles regularly arranged becomes small according as the recording density of patterned medium becomes high.
In addition, in the method of allowing the magnetic material formed as film on the upper surface of the projection to be recording part, magnetic material is formed as film also between each recessed part between projections so that magnetic coupling takes place between the magnetic material within the recessed part and the magnetic material on the upper surface of the projection. For this reason, it is a task to completely separate such magnetic coupling.